This invention relates to an adjustable steering column for a vehicle having a clamping mechanism with a clamp bolt assembly.
The steering columns are rake and/or reach adjustable to suit the comfort of the driver. A clamping mechanism is employed to release the steering column to facilitate such rake and/or reach adjustment of the steering wheel and is then clamped, usually by a clamping lever, to hold the steering column in its adjusted position.
Typical clamp systems comprise components assembled laterally to the longitudinal installation/adjustment axis of the steering column, which are designed to convert driver-initiated rotational clamp/unclamp lever motion into tensile load in a clamp bolt in conjunction with a lever cam and cam follower or screw lift system. This tensile load is subsequently reacted as compressive clamp pressure between an adjacent slidable clamp bracket and static column bracket surfaces so as to produce a static friction break away force reaction to controlled limits.
A common problem associated with the operation of such clamp systems arises from loss in the actual performance of the actual clamping push load applied to the clamping components within the expected operational life of the vehicle due to load-generated creep in load bearing thermoplastic components, for example, surface-to-surface component wear and variable compressive stiffness in the structural supports, each of which has the effect of reducing the axial strain and thus tensile load generated in the clamp bolt and consequent loss of control of the static friction break away force.
According to the present invention, there is provided an adjustable steering column clamping mechanism having a clamp bolt assembly, the assembly including a substantially cylindrical rod with two ends, one end having a reduced diameter portion to receive a plurality of disc springs, a shoulder thereby being formed between the reduced diameter portion and the adjoining portion of the rod and there being means to place a primary load on the disc springs to put them into compression on the rod; the arrangement being such that, when the rod is placed under tension between its ends, the disc springs provide a substantially constant secondary load function to compensate for any loss of tensile load in the rod.
The end of the rod remote from the disc springs may be threaded.
The means to place a primary load on the disc springs may be a nut. The nut may be held in place by preening said one end of the rod over the nut. The nut may be a nut blank.
There may be a minimum of two disc springs and may be in a series or a parallel stack in multiples of two disc springs.
Said one end of the rod may be provided with a further reduced-diameter portion that extends from the extremity of the rod to the first mentioned reduced diameter portion. This further reduced-diameter portion may be roughen ed, such as by diamond knelling.
The clamping mechanism may be of the type that applies a primary clamping load on the clamp bolt assembly by means of at least one cam. Alternatively, the clamping mechanism may apply a primary clamping load on the clamp bolt assembly by means of a screw lift device.